Can't really say definitely; still haven't received the transformer that is suitable to drive it directly. My suspicion is though, it's the ISO 3.3v / Reflektor-D that's elevating the performance the most over say the 3.3v as tapped from an Amanero. My experience say that the SSR03 is helping a bit too. Time and again engineers build PS's onboard they believe do not lack, and yet can be improved upon (even in a pre-reg configuration such as this).
I'm listening to it now running Pauls minimum phase filter and there's no harshness, wide accurate sound stage, very good.
So when the dust settles, I suspect it'll be both - very good DC supplies + the right filters.
Soren hinted at a version without onboard PS's or output circuits - hope he gets to it; that'll really allow builders to play. But as it is, this DAC will certainly stay in my rotation.